The present invention relates to a process for producing polyalcohols. More particularly, the present invention relates to a process for producing polyalcohols by hydrogenating polyketones, which are copolymers of carbon monoxide and at least one olefin. The polyalcohols produced by the present invention may be used as, for example, gas-barrier materials, such as packaging materials.
It is known in the art to produce polyalcohols by hydrogenating copolymers of carbon monoxide and olefins in the presence of heterogeneous or homogeneous catalysts. Among processes employing heterogeneous catalysts, Japanese Laid-open Patent Publication Nos. 149828/1989 and 232228/1990 disclose nickel catalysts, such as Raney nickel or metallic nickel, either as is or carried on diatomaceous earth, silica, alumina or the like; Adkins catalysts, such as CuO/Cr.sub.2 O.sub.3 and CuO/Cr.sub.2 O.sub.3 /BaO; cobalt catalysts, such as Raney cobalt and CuO/SiO.sub.2 ; ruthenium catalysts, such as Ru/carbon, Ru/Al.sub.2 O.sub.3 and Ru/SiO.sub.2 ; palladium catalysts, such as Pd/carbon and Pd/SiO.sub.2 ; and similar catalysts. Japanese Laid-open Patent Publication No. 339367/1993 discloses catalysts comprising a metal such as nickel, ruthenium or platinum, ruthenium oxide, Raney nickel, Adkins catalysts and the like, and preferably ruthenium carried on a-alumina or ruthenium oxide. Japanese Patent Publication No. 49203/1994 discloses a ruthenium catalyst carried on alumina having an average micropore radius of at least 100 angstroms. Japanese Laid-open Patent Publication No. 204929/1989 discloses a reduced nickel catalyst produced by reacting a metal hydride with a nickel compound.
Among processes employing homogeneous catalysts, Japanese Laid-open Patent Publication Nos. 149828/1989 and 23222811990 disclose catalysts comprising ruthenium complexes, such as dichlorotris(triphenylphosphine) ruthenium and dihydridotetrakis(triphenylphosphine) ruthenium; rhodium complexes, such as chlorotris(triphenylphosphine) rhodium; and the like. Japanese Laid-open Patent Publication No. 339367/1993 discloses catalysts comprising chlorotris(triphenylphosphine) rhodium, dichlorotris(triphenylphosphine) ruthenium, ruthenium dodecacarbonyl and the like.
To obtain polyalcohols having good gas barrier properties, it is necessary to maximize the content of hydroxyl groups in the obtained polyalcohols. It is also desirable to minimize the amount of catalyst required for commercial application of the process, due to catalyst cost.
The above prior art processes for producing polyalcohols have two principal disadvantages. First, these processes require large amounts of catalyst. For example, Japanese Laid-open Patent Publication No. 149828/1989 uses a heterogeneous catalyst comprising a nickel-rhenium catalyst in an amount of 2 g per 5 g of a polyketone copolymerized from ethylene and carbon monoxide. Japanese Laid-open Patent Publication No. 232228/1990 uses a heterogeneous catalyst comprising a copper/chromium/manganese/barium catalyst for a polyketone copolymer of ethylene, propylene and carbon monoxide, in an amount of the same weight as that of the polyketone. Japanese Laid-open Patent Publication Nos. 339367/1993 and 49203/1994 disclose a ruthenium/.alpha.-alumina catalyst in an amount of 8 g per 5 g of a polyketone copolymerized from ethylene and carbon monoxide. It is clear that such large amounts of catalysts, relative to the amounts of the reactants, are economically undesirable.
Second, these processes may result in poor selectivity of hydrogenation, that is, these processes are incapable of maximizing the content of hydroxyl groups in the products. Poor selectivity is caused by the formation of tetrahydrofuran rings in the product of the reaction. The tetrahydrofuran rings are formed from hemiacetals, which are formed by partial reduction of the carbonyl groups in the polyketones to form hydroxyl groups. The hydroxyl groups then react with the carbonyl groups, thereby decreasing the hydroxyl group content. Japanese Laid-open Patent Publication No. 204929/1989 discloses a process in which a reduced nickel catalyst is used to hydrogenate a copolymer of ethylene, propylene and carbon monoxide. In this process, about 0.9 g of the nickel compound is required per 10 g of the copolymer polyketone. Although this amount of catalyst is relatively small, compared to other conventional methods, the polyalcohol produced by this process contained 13% residual carbonyl groups and 17% tetrahydrofuran rings. It is thus virtually impossible to produce a polyalcohol having a high hydroxyl group content, and therefore good gas barrier properties, using this process.
Japanese Laid-open Patent Publication No. 304122/1989 describes a process which comprises hydrogenating a polyketone copolymerized from ethylene and carbon monoxide using a catalyst comprising a ruthenium-carbonyl complex and an iodide. The product of this reaction is a polymer comprising ethylene units and tetrahydrofuran ring units. The use of this ruthenium catalyst therefore leads principally to formation of tetrahydrofuran rings, and no polyalcohol at all.
The use of homogeneous catalysts, such as dichlorotris (triphenylphosphine) ruthenium, is described in Japanese Laid-open Patent Publication Nos. 149828/1989, 232228/1990 and 339367/1993. None of these applications, however, report any experiments using these catalysts to produce polyalcohols. The present inventors therefore attempted to conduct hydrogenation using dichlorotris(triphenylphosphine) ruthenium, as described in the above applications. However, as shown in Comparative Example 1, these processes could not produce a polyalcohol with high yield and selectivity.